1. Field of the Invention
The present invention relates to a navigation system, and particularly relates to a navigation system having a route-guidance function for searching a most suitable guidance route from the current point to a destination and guiding a driver along the searched guidance route.
2. Description of the Related Art
In general, known navigation systems for vehicle travel guidance not only display a map of an area around the current position but also specify a destination, thereby automatically setting a guidance route from the current position to the destination for guiding the driver. According to this route-guidance function, a simulation according to the breadth first search (BFS) method or the Dijkstra method is performed, whereby a route with the smallest cost from the current position to the destination is automatically searched by using map data. This searched route is determined to be the guidance route.
After the guidance route is determined, the guidance route is displayed by a thick line having a predetermined color different from that of other routes, so as to distinguish the guidance route from the other routes on a map image while the vehicle is traveling. When a distance between the vehicle and a guidance intersection on the guidance route has a predetermined or smaller value, predetermined intersection guidance is provided for guiding the driver to the destination. This intersection guidance includes an intersection guidance image including an enlarged intersection image and an arrow image for indicating a direction along which the driver should travel, and travel direction guidance by voice, for example.
The destination can be determined by moving a cursor on the map image, or selecting a predetermined point from among a destination menu list. According to the former method, a user operates a remote control or the like, thereby scrolling the map image, putting the cursor on a predetermined point and setting the point, as the destination. According to the latter method, the user selects and inputs a keyword such as a facility name, a point name, a telephone number, an address, a zip code, and so forth, through a menu image, thereby searching a predetermined point. Then, the user determines the searched point to be the destination.
Where the former method is used, the user must correctly know the location of a point that is to be set as the destination. On the other hand, where the latter method is used, the user must know at least one of the facility name, phone number, address, zip code, and so forth, even though the user does not know the location of the point that is to be set as the destination.
However, the user often does not know the location or facility name of the point, even though he/she knows the building or scenery of the point that is to be set as the destination. In this case, it is not possible to search the point and determine the destination by using the point search function of the known navigation systems. Therefore, a new point search method is needed for allowing a destination to be determined in the above-described case.
In the past, technologies for extracting the feature amount of an object image from image data, identifying an object by searching information about the extracted feature amount, and displaying various information about the identified object, as a search result, have been known. An example of the above-described technologies is disclosed in Japanese Unexamined Patent Application Publication No. 2000-113097.
As has been described, the known navigation devices can perform point search by using information including the facility name, area name, telephone number, address, zip code, and so forth, of a point which is to be set as a destination, as a keyword. Therefore, where the above-described information is not provided, the known navigation systems cannot perform the point search, whereby the destination cannot be determined.